Optimal Throughput Fairness Tradeoffs for Downlink Non-Orthogonal Multiple Access over Fading Channels

Hong Xing, Yuanawei Liu, Arumugam Nallanathan, Zhiguo Ding, H. Vincent Poor

Research output: Contribution to journalArticlepeer-review

54 Scopus citations


Recently, non-orthogonal multiple access (NOMA) has attracted considerable interest as one of the 5G-enabling techniques. However, the users with better channel conditions in downlink communications intrinsically benefit more from NOMA than the users with worse channel conditions thanks to successive decoding, judicious designs are required to guarantee user fairness. In this paper, a two-user downlink NOMA system over fading channels is considered. For delay-tolerant transmission, the average sum rate is maximized subject to both average and peak-power constraints as well as a minimum average user rate constraint. The optimal resource allocation is obtained using the Lagrangian dual decomposition under full channel state information at the transmitter (CSIT), while an effective power allocation policy under partial CSIT is also developed based on analytical results. In parallel, for delay-limited transmission, the sum of delay-limited throughput (DLT) is maximized subject to a maximum allowable user outage constraint under full CSIT, and the analysis for the sum of DLT is also performed under partial CSIT. Furthermore, an optimal orthogonal multiple access (OMA) scheme is also studied as a benchmark to prove the superiority of NOMA over OMA under full CSIT. Finally, the theoretical analysis is verified by simulations via different tradeoffs for the average sum rate (sum-DLT) versus the minimum (maximum) average user rate (outage) requirement.

Original languageEnglish (US)
Pages (from-to)3556-3571
Number of pages16
JournalIEEE Transactions on Wireless Communications
Issue number6
StatePublished - Jun 2018

All Science Journal Classification (ASJC) codes

  • Computer Science Applications
  • Electrical and Electronic Engineering
  • Applied Mathematics


  • Lagrangian dual decomposition
  • Non-orthogonal multiple access
  • ergodic rate
  • fading channel
  • fairness
  • orthogonal multiple access
  • outage probability
  • strong duality


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